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Darwin, Charles

Charles Robert Darwin (1809–1882) is widely considered the greatest
naturalist of the nineteenth century. His pioneering work in the theory of
evolution wrought a revolution in the study of the origins and nature of
plant and animal life.

The son of Robert Darwin, a prominent English physician, Charles had an
early interest in natural history, especially hunting, collecting, and
geology. At his father's urging, Darwin attended medical school at
Edinburgh, but found that he had little interest in medicine and returned
home after two years. Wanting his son to have a respectable career,
Darwin's father suggested that he should become an Anglican
clergyman. Because the quiet, scholarly life of the clergyman appealed to
him, Darwin agreed. He completed his degree at Cambridge in 1831. While
awaiting an assignment, he was recommended for the job of naturalist on
the survey ship
Beagle,
a voyage of nearly five years. In 1859 Darwin published
The Origin of Species by Means of Natural Selection
based on his discoveries during this voyage.

This seminal work contained three major discoveries. First, it presented
an overwhelming amount of physical evidence of Darwin's
evolutionary thesis. Naturalists had observed evolutionary change since
the time of the ancient Greeks, and by the mid-1800s the idea of evolution
was "in the air." But it was not until Darwin published
Origin
that a body of empirical evidence supported the idea of evolution.
Because of Darwin's thorough and compelling work, almost no
biologists today doubt the reality of evolution. Second, Darwin discovered
descent from common ancestry, demonstrating that all living things are
related. Tracing the lineage of any two species back far enough, one can
find a common ancestor. The modern fossil record and biochemical
comparisons among species verify this observation. Earlier theorists such
as Jean Baptiste de Lamarck had assumed that life had originated many
times and that each lineage was unique and unrelated to all others. Third,
Darwin discovered and described the basic mechanism by which evolution
works: natural selection. Natural selection is the differential
reproductive success of some individuals in a population relative to that
of others.

The Darwinian mechanism is based on differential reproductive rates.
First, natural populations exhibit variation in phenotype (physical
makeup) from one individual to the next, and this variation is genetically
determined. For example, there is

Modern biologists recognize other evolutionary processes not known
to Darwin, but natural selection remains the basic mechanism.

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considerable variation in human height, skin color, and so on, within a
population.

Second, organisms are genetically programmed to reproduce. Reproduction is
a very powerful biological urge, and animals will risk or even sacrifice
their lives to accomplish it. Humans feel this genetic programming in
several ways, as a ticking "biological clock," as parental
instinct, or as an attraction to children. As a result, natural
populations have a tendency to overpopulate. Biologists define
"overpopulation" in terms of limiting factors that may
include food, space, mates, light, and minerals. For example, if there is
enough space on an island for 1,000 deer but only enough food to sustain a
population of 100, then 101 deer constitutes overpopulation. The result of
overpopulation is competition among the individuals of the population for
the limited resources. If there are no limited resources, there is no
competition. Competition results in "survival of the
fittest," an unfortunate phrase that Darwin borrowed from
contemporary social theorists who are now known as "social
Darwinists." In Darwinian terms, however, fitness
refers only to reproductive success, not to strength, size, or (in
humans) economic status.

Third, some of the variants in the population are more efficient than
others in exploiting the limited resources. Success in obtaining limited
resources is due largely to inherited phenotype. These individuals channel
more of the limited resource through themselves and are therefore able to
reproduce more successfully than individuals that compete less
successfully. Thus, these selected variants pass on their genes for their
genotype with greater frequency than do other variants.

Fourth, the result of this selectively favored breeding is a modification
of population gene frequencies over time that may cause a change in
phenotype. That is, the average state of a given character undergoing
selection changes from one generation to the next. If, for example,
predators feed on slower antelope, the average running speed of the
population will gradually increase from generation to generation. This is
observed as evolution.

And lastly, the losers, those individuals less successful at exploiting
limited resources and at reproduction, may die in greater numbers (if, for
example, they do not find enough food) or may find an alternative to the
limited resource. Galapagos finches (Darwin's finches) with thinner
beaks that were less successful at eating heavy seeds often found
alternative foods such as insect larvae, which are more accessible to
thinner beaks. Over time, this process results in evolutionary
diversification of an ancestral species into two or more progeny species,
the divergence from common ancestry recognized by Darwin.

Darwin had three great accomplishments with the publication of
Origin of Species
in 1859. He produced an overwhelming body of physical evidence that
demonstrated the fact of evolution. Darwin also discovered descent from
common ancestry and, lastly, the basic mechanism by which evolution
operates—natural selection based on differential reproductive rates
of individuals in a breeding population. The implications of
Darwin's discoveries have profoundly influenced almost every area
of knowledge from science to religion to social theory.